CELL MEMBRANE COMPLEX 447 A PROPOSAL FOR THE STRUCTURE OF THE CUTICLE–CORTEX CMC The following proposal for the cuticle–cortex CMC (Figure 7) is based on logic and the following supporting evidence. The work of Nakamura et al. (8) suggests that the cuticle– cortex CMC differs from both the cuticle–cuticle CMC and the cortex–cortex CMC. The work of Leeder et al. (44) and of Mansour and Jones (37) shows that the cuticle– cortex CMC is more resistant to solvents than the cortex–cortex CMC. But the most convincing evidence for this model (Figure 7) is the uranyl dye study by Leeder et al. (50) which showed layers of dye around each cuticle cell, i.e., two layers of dye in the cuticle– cuticle CMC, one layer of dye in the cuticle–cortex CMC, and no layers of dye in the cortex–cortex CMC. Since the cuticle–cortex CMC bridges cuticle and cortical cells, it is logical to assume that it is a hybrid based partly on the cuticle–cuticle CMC and the cortex–cortex CMC. Therefore, the membrane on the cuticle side would be the cuticle cell membrane that supports covalently bound fatty acids that are bonded either through thioester, ester, or amide linkages, and these covalently bound fatty acids are connected on their hydropho- bic end to a hydrophobic protein in the delta layer. The membrane on the cortex side is a cortical cell membrane that supports fatty acids bound through polar and salt linkages, as illustrated in the schematic of Figure 7, and these fatty acids form a lipid bilayer. The delta layer of the cuticle–cortex CMC should then contain a hydrophobic protein on one side (to bond to the beta layer on the cuticle side) and a hydrophilic protein on the opposite side (to bond through polar and salt link- ages to the lipid bilayer). Leeder et al. (50) in their TEM study on dyeing and diffusion suggested that either the cuticle beta layer or the resistant membrane surrounding cuticle cells has an affi nity for the uranyl dye, whereas the cortical cell membrane or the delta layer between cortical cells does not. The models in Figure 7 (for the cuticle–cortex CMC), Figure 2 (for the cuticle–cuticle CMC), and Figure 3 (for the cortex–cortex CMC) are consistent with the results and explanation by Leeder et al. (50) of the uranyl dye binding in the three different CMCs. Figure 7. Schematic representing the cuticle–cortex CMC (not drawn to scale).

JOURNAL OF COSMETIC SCIENCE 448 THE FORMATION OF THE CMC IN DEVELOPING HAIRS The following description of the formation of the CMC in the developing hair fi ber was taken from the work of Rogers (53), and also from the early work by Orwin and cowork- ers (54), with more recent work by Jones and coworkers (55). For more details of the formation of the CMC in developing hair fi bers, I recommend the review by Jones and Rivett (11) and the recent paper by Jones et al. (55). In the latter stages of development of the hair fi ber, desmosomes or intercellular bridges, gap junctions (where cells exchange molecules), and tight junctions (intercellular junc- tions where cell membranes fuse) are established between differentiating keratinocytes of the hair fi ber and the inner root sheath to varying extents as they move upward in the hair follicle (see Figure 8). Orwin et al. (54) observed that gap junctions and desmosomes cover about 10% of the plasma membrane of cortical cells in the bulb region and then gradually degenerate. Tight junctions are established between Henle’s outermost layer of the inner root sheath and Huxley’s layer of the inner root sheath and between Henle cells and the close com- panion layer of the outer root sheath (see Figure 8). These junctions are replaced with a new cell membrane complex that gradually develops as a continuous complex between the cells. Similar events should occur for cuticle–cuticle CMC, cuticle–cortex CMC, and cortex–cortex CMC, with appropriate distinctions to allow for the differences that arise between these three different cell-connecting units. LIPIDS OF THE CMC OF KERATIN FIBERS METHODS TO REMOVE LIPIDS FROM ANIMAL HAIRS FOR ANALYSIS Removal of external lipids. Wool fi bers are normally processed by scouring with a nonionic agent such as Lissapol TN 450 (a nonylphenol ethoxylate with an average of 8.5 ethoxy units CTFA = nonoxynol-8.5) and then in scientifi c studies treated with one or more solvents to remove any remaining external lipids. Non-swelling solvents and/or solvents of bulky molecules (like t-butyl alcohol) have been used to remove external lipids from keratin fi bers, that is, lipids that are believed to be soil and not part of the internal structure of animal hairs. Solvents such as hexane, t-butyl alcohol, or heptane, and sometimes Figure 8. Schematic of the different layers of an active hair follicle (not drawn to scale).